From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 1AFF7596 for ; Sun, 11 Dec 2016 19:55:39 +0000 (UTC) X-Greylist: whitelisted by SQLgrey-1.7.6 Received: from mail-ua0-f182.google.com (mail-ua0-f182.google.com [209.85.217.182]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 3F1301A1 for ; Sun, 11 Dec 2016 19:55:36 +0000 (UTC) Received: by mail-ua0-f182.google.com with SMTP id 12so64502314uas.2 for ; Sun, 11 Dec 2016 11:55:36 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:from:date:message-id:subject:to; bh=65zS5Tvehc8EzoNJg36Rccui+gShaUE9BZXOFb13uRA=; b=kP0nUqB0tCHQO+bBDXEr5Kj1Xr2hpMNai8oMJpjyIOqjUIYDrnDok6J6SzX5k+4Kt3 nir+bjFcn49r7f/lwFw2sbL1vmVzOa0/nCOry6V66lXP16XONE/bbI0oAvJuLm9+dqDt TssRDQFYi4kFPs0rq84rHeUdZsJ5KY1tziN9959Xv/2m0J2OHICZuGYHop4sX4fDfb6l aFQLZK6UD2oMmwT0GNkG32+0ftL2kdbN9qER4vsSwRxbSrVF+UQci2cetnhYESdHRvgB 4JcvxAECrhi9WGh8ACe7Uhfgw4lj/LwzLkt2qhiC3vHzSnk4hA4NaaGbjd53hxU101Lm KEvA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to; bh=65zS5Tvehc8EzoNJg36Rccui+gShaUE9BZXOFb13uRA=; b=JNcc65VN+nYveAzaCSxH7l6kUwTbPg0Cy90GiJ+1WA0Ql9zJvpf8i6KOQJDT4zeuqX 70rI3n3IWTHRa1mHmfPj531AR1y7U9XtP5ZYrQqIxyQGAIvTqPiTONFA6Lynj1Ca29nO SYFiYOCOYITv5znKhu5HSVruiRFIR2Yod5RPyAKL5b6+e+DnkomgRyJC+midWy62S4rG pFg9HfnVlt1Y05ExzmCM7kfQgsM9VyU6yOJ5vV/j66XIE5MZs6oVzEmz7uTjR/4OhIkb eh2rxbK5+Pyqgj88MNJGkU14ItloyRJHvyOz2M5ZHIsFIizQtfyzYxrYs2hwTV+5ZT2+ 5jng== X-Gm-Message-State: AKaTC03itHZgyk59TWcw/05LaL8yQg4FVUMlhQ+dFhObVHvdXnglrTnyuJyTA90Mk9+2bwp8xDO2WnGSVSoIkA== X-Received: by 10.176.86.23 with SMTP id y23mr55546673uaa.88.1481486135361; Sun, 11 Dec 2016 11:55:35 -0800 (PST) MIME-Version: 1.0 Received: by 10.103.49.144 with HTTP; Sun, 11 Dec 2016 11:55:34 -0800 (PST) In-Reply-To: References: From: "t. khan" Date: Sun, 11 Dec 2016 14:55:34 -0500 Message-ID: To: s7r@sky-ip.org, Bitcoin Protocol Discussion Content-Type: multipart/alternative; boundary=f403045daa66d685880543675e46 X-Spam-Status: No, score=-0.0 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_ENVFROM_END_DIGIT,FREEMAIL_FROM, HTML_MESSAGE, RCVD_IN_DNSWL_NONE, URIBL_BLACK autolearn=no version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on smtp1.linux-foundation.org X-Mailman-Approved-At: Sun, 11 Dec 2016 20:18:21 +0000 Subject: Re: [bitcoin-dev] Managing block size the same way we do difficulty (aka Block75) X-BeenThere: bitcoin-dev@lists.linuxfoundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Bitcoin Protocol Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 11 Dec 2016 19:55:39 -0000 --f403045daa66d685880543675e46 Content-Type: text/plain; charset=UTF-8 On Sun, Dec 11, 2016 at 12:11 PM, s7r wrote: > > This is an incentive, if few miners agree to create a large conglomerate > that will ultimately control the network. > > You miss something obvious that makes this attack actually free of cost. > Nothing will "cost them more in transaction fees". A miner can create > thousands of transactions paying to himself, and not broadcast them to > the network, but hold them and include them in the blocks he mines. The > fees are collected by him because transactions are included in a block > that he mined and the left amount is in another wallet of the same > person. Repeat this continuously to fill blocks. > No, that wasn't overlooked. Miners could indeed stuff their own blocks for free, but they can't stuff blocks mined by others for free. In the hypothetical scenario where there is a single mining pool which mines most (if not all) of the blocks, we would have much larger problems than their ability to raise the max block size gradually. Even if they were able to fill 100% of the blocks for an entire year, the max block size for that 2016 block period would be 7.25MB (not accounting for SegWit). After the whole year they would have made no extra profit vs doing nothing. And as soon as they stopped this scheme, block size would spring back to it's natural level. The good news is, this scenario has never happened and even when we've come remotely close (when ASICs first shipped), the situation was temporary. The odds of this happening in the future and persisting long enough to have any major effect with Block75 are very close to zero. > Topology and bandwidth speed / hash rate of the network cannot be > controlled - if we make assumptions about these it might have terrible > consequences. > > Even if we take in consideration that bandwidth will only grow and disk > space will only cost less (which is not something we can safely assume, > by the way) the hard limit max. block size cannot grow to unlimited > value (even if the growth happens over time). There is also a validation > cost in time for each block, for the health of the network any node > should be able to download _and_ validate a block, before next block > gets mined. > > You said in another post that a permanent solution is preferred, rather > than kicking the can down the road. I fully agree, as well as many > others reading this list, but the permanent solution doesn't necessarily > have to be increasing the max block size dynamically. > Increasing *and* decreasing max block size dynamically. Block75 is self-correcting, whereas any solution with hardcoded limits can't correct without human intervention and would rely on our ability to predict the future (which as you pointed out, we can't do). Therefore, any solution that's not dynamic cannot be permanent. Additionally, the frequent and gradual changes in max block size would allow us to see any consequences well in advance (years probably). > If you think about it the other way around, dynamically growing the max > block size is also kicking the can down the road ... just without having > to touch it and get dust on the boot ;) Not having to touch it again = permanent solution. ;) It would be helpful if some others would run the numbers on how Block75 would adjust the block size over time: new max block size = 1000kb + (average block size over last 2016 blocks - 750kb) -t.k. --f403045daa66d685880543675e46 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable

= On Sun, Dec 11, 2016 at 12:11 PM, s7r <s7r@sky-ip.org> wrote:

This is an incentive, if few miners agree to create a large conglome= rate
that will ultimately control the network.

You miss something obvious that makes this attack actually free of cost. Nothing will "cost them more in transaction fees". A miner can cr= eate
thousands of transactions paying to himself, and not broadcast them to
the network, but hold them and include them in the blocks he mines. The
fees are collected by him because transactions are included in a block
that he mined and the left amount is in another wallet of the same
person. Repeat this continuously to fill blocks.

No, that was= n't overlooked. Miners could indeed stuff their own blocks for free, bu= t they can't stuff blocks mined by others for free.

In the hypothetical scenario where there is a single mining pool whic= h mines most (if not all) of the blocks, we would have much larger problems= than their ability to raise the max block size gradually. Even if they wer= e able to fill 100% of the blocks for an entire year, the max block size fo= r that 2016 block period would be 7.25MB (not accounting for SegWit). After= the whole year they would have made no extra profit vs doing nothing. And = as soon as they stopped this scheme, block size would spring back to it'= ;s natural level.

The good news is, this scenario = has never happened and even when we've come remotely close (when ASICs = first shipped), the situation was temporary. The odds of this happening in = the future and persisting long enough to have any major effect with Block75= are very close to zero.
=C2=A0
Topology an= d bandwidth speed / hash rate of the network cannot be
controlled - if we make assumptions about these it might have terrible
consequences.

Even if we take in consideration that bandwidth will only grow and disk
space will only cost less (which is not something we can safely assume,
by the way) the hard limit max. block size cannot grow to unlimited
value (even if the growth happens over time). There is also a validation cost in time for each block, for the health of the network any node
should be able to download _and_ validate a block, before next block
gets mined.

You said in another post that a permanent solution is preferred, rather
than kicking the can down the road. I fully agree, as well as many
others reading this list, but the permanent solution doesn't necessaril= y
have to be increasing the max block size dynamically.
=
Increasing *and* decreasing max block size dynamically. Bloc= k75 is self-correcting, whereas any solution with hardcoded limits can'= t correct without human intervention and would rely on our ability to predi= ct the future (which as you pointed out, we can't do). Therefore, any s= olution that's not dynamic cannot be permanent.

Additionally, the frequent and gradual changes in max block size would al= low us to see any consequences well in advance (years probably).
= =C2=A0
If you think about it the other way around, dy= namically growing the max
block size is also kicking the can down the road ... just without having to touch it and get dust on the boot ;)

Not= having to touch it again =3D permanent solution. ;)

It would be helpful if some others would run the numbers on how Block75 = would adjust the block size over time:

new max blo= ck size =3D 1000kb + (average block size over last 2016 blocks - 750kb)

-t.k.

--f403045daa66d685880543675e46--